Ashen,

I'm in a mixed orientation marriage. We're married 37 years, monogamous, and in all respects (including sexual) a relation that makes us both happy. Though I do understand your current situation, because after my wife came out as lesbian (17 years ago), it was very difficult and confusing for us as well. 
If you're interested how we went through it, you can read a lot about our story in the "strategies for MOMs" section:

https://straightspouse.boardhost.com/viewtopic.php?id=1931
https://straightspouse.boardhost.com/viewtopic.php?id=2114
If you've questions please post in these topics. (esp. because my wife can only reply in her own topic there) 

Sonnet,

your wife is lesbian, in that sense it's to be expected she's not physically attracted to you being a man. Her sexual preference is directed towards the female form.
I get the impression she's beating about the bush, by refering to you as getting older, even the abuse in childhood is (probably) smoke screen. Maybe in an attempt to soften the message, as she also tries not to hurt your feelings. But also making it easier to herself to express that sex isn't the thing for her, and hopes it's off the table.
Well, she succeeded in that. But she's in the dark what you really feel and what consequences this all has for you.
She doesn't understand you really, and knows not what you feel nor what you felt all those years in marriage. Maybe just in a general abstract way that you liked sex and enjoyed it more than she did.
To her, putting intimacy on hold is not that different situation as it was before. Being sometimes physical pleasurable, but emotionally without deeply felt connection.
Chances are she assumes this is about the same for you (with nothing in herself to compare it to). True, you'll have to cope with your male libido, but nothing near what the real emotional consequences for you are.
Like you are missing an essential part of what you want to share and experience in a relation with someone you love. 

Are you talking regulary with each other about the problems? For it's quite something you're going through. 
If so are you clear enough to your wife about what you feel. Or very cautious not to hurt her feelings, empatizing with her so much that you rather take the consequences on your shoulders.
But what about your feelings and expectations of marriage? 
You both went to couples therapy, was the result of these sessions that you simply had to learn to cope with the situation? Nothing about what your wife could do to work towards a solution for the situation? 
When did the "abuse in childhood argument" came into play? It's a bit odd that only after 1

JRW,

If I understand you correctly, your wife has single sidedly decided she want's an open relation om her side, you are expected to follow along...
Didn't she question the ethics of her conduct or how her actions would impact you?
You ask how long that would work? Well, I would suggest: zero days, for this is not how someone would treat someone they supposedly love.

Are LBG different kind of humans, that are above questioning the morals of their behaviour? There is a trope of this kind of reasoning in western culture.
Totally non-sense of course, but many fall for it (subconsiously). The highest moral standard is "following your feelings and living it out", and that trumps everything else.
Well... that leaves you with nothing, you should wave the rainbow flag while your wife lives out her desires.
Is that part of the reason you are even considering to endure this ordeal?

What if your wife was straight and she went out on tinder, matched with a man there. And the same line of story unfolded. Would you even consider enduring that too? 

The fact in your situation it's about same sex, doesn't change anything at a fundamental level. She's cheating and actively persues an adultery livestyle. Period!
Draw the line!

Dutchman.

I think the MOM acronym is okay. Mixed Orientation Marriage, is accurately enough to define the situation. I suppose most people will understand what it stands for. It isn't ideal, but I haven't encountered any other acronym that is more clear.
 
The "fluffy ducks happy" annotation you suggest isn't at all obvious to me. So this may be a personal thing/impression of you? 
Then again, some people create a disturbed watered down image of a relation, that should pass as marriage, of which I wonder why it's called marriage at all. So, if that's what you mean?

Hi BOFA,

what you both have to work through is quite a lot. Coping with finding yourself in a MOM situation is complicated. For you, and for your husband. Both have to deal with feelings, questions and pain. 
We certainly weren't excluded from that, sometimes it was so very very difficult. Reading your post, I so much understand the predicament you're going through. I just have to close my eyes and think back to those years, and feel the hurt of that situation again.

The only way that I can try to really help you, is by telling our story and how we got to a solution. Providing hope but also knowledge to get to where you want to find yourself. We had to find our way without any guidance or outlook, so I hope it makes a difference in that regard. But it will not avoid the painful experience you both have to go through. It has to go to the real fundaments of love, total acceptance, complete authenticity.
Just "somewhere in the general direction" won't do, it has to be really real and heartfelt. That's what makes the journey so hard, no shortcuts are allowed. (well... you'll probably tried or still try, but it won't work).

It's a joint venture, you both have to go this way. Each with their own specific package of trouble. The straight has other kind of troubles to deal with than the gay has to. And a man has other kind of problems as compared to a woman. One is not harder than the other, it's only different. Each has to cope with their own personal challenge. However, you can (and should) try to understand and support each other, but each has also an individual path to go. Next to the common goal you go for as a team, that aims at getting the marriage to what and where you both want it to be.

The goal of a succesful MOM is not "some lesser than". If anything, a succesful MOM is more than you expected or thought. For when you get through the huge obstacles, you have a relation that goes beyond most marriages, and with a depth that many relations never achieve. And i